Breast milk is a source of nutrition for many human infants. Breast milk is recommended as a source of nutrition for infants by the World Health Organization, the Centers for Disease Control and the American Academy of Pediatrics. In addition to purported health benefits for the nursing mother and child, direct nursing can be a cheap or cost-free method of feeding an infant. In direct nursing, the suckling action of the infant's mouth can induce the release of oxytocin into the bloodstream. Oxytocin can make the muscles around the mammary glands in the breasts contract, pushing milk into the milk ducts and out through nipple openings in what is known as the milk ejection reflex. The milk ejection reflex starts a flow of milk that can be consumed by the infant.
Direct nursing is not always possible or preferable for the mother or child. Even when mothers are physically capable of nursing, direct nursing requires the mother to be available to feed the infant multiple times per day. In addition, the mother's milk production schedule may not be optimal for the infant's needs. Breast pumping technology has enabled mothers to express milk for storage and later feeding. The infant can be fed stored milk when needed by the mother, a non-birthing parent, or a caregiver. Milk storage can also provide human breast milk to infants who are unable to receive it from their birth mothers (for example, in cases of adoption, or undersupply).
Conventional breast pumps rely on a suction mechanism provided by a powered vacuum or hand pump. These pumps generally comprise a roughly hemi-spherical dome that can be placed over the nipple-areolar complex and a tube or other conduit for expressed milk to be pumped from the breast to a collection mechanism (such as a bottle, jar, or pouch). One disadvantage of conventional breast pumps is the need to disrobe sufficiently to expose the nipple. In addition, while hand-powered pumps can be quiet, they are generally slow, and require a significant amount of physical exertion by the user. Electrically powered breast pumps can be faster (especially those that are capable of expressing milk from both breasts simultaneously), but are often undesirably noisy. Users therefore often require a private space in which to pump, and are generally prevented or distracted from other activities during the pumping process. Furthermore, suction-based pumps can produce up to ten times the amount of suction that an infant applies while suckling. This increased level of suction often leads to discomfort and pain.
Another method for expressing breast milk is known as manual expression. Instead of the suction action of a pump, the hands are used to applying pressure to the breast tissue in patterns that induce the flow of milk, which can be collected in a container. In addition to cost, manual (or “hand”) expression can be advantageous because pressure can be applied selectively to focus on particular areas of the breast. Many women have particular areas of the breast that are more productive of milk, and these areas can change over time. Manual expression is also thought to affect the nutritional content of the milk. Studies have shown that hand expressed milk has higher fat concentrations than suction pump expressed milk. This may be due to a retrograde milk flow within the breast. Milk can flow from the breast, toward the chest wall, before exiting at the nipple-areolar complex. This retrograde flow, which is presumed to be enabled by an infant's suckling pattern, can allow for the backwash of milk into the originating alveoli which can carry the higher density milk that contains higher fat concentrations.